Longtime Senator Arlen Specter holds a 13-point lead over his Democratic Primary challenger Joe Sestak.

A new Rasmussen Reports telephone survey of likely Pennsylvania Democratic Primary voters finds Specter beating Sestak 48% to 35%. Three percent (3%) of primary voters favor some other candidate, and 14% remain undecided.

In each of the last four polls, Specter’s support has stayed between 46% and 51%. That’s troubling territory for a long-term incumbent but not necessarily disastrous.

Sestak’s support has ranged from 32% to 42% in all four polls. He was most competitive in October when the numbers showed Specter with 46% of the vote and Sestak at 42%.

Specter currently leads by 20 points among female primary voters. Male voters are almost evenly divided between the two candidates. Voters 50 and older prefer Specter more than those who are younger.

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Specter was a Republican senator for nearly 30 years, but he switched parties in April just after a Rasmussen Reports poll showed him trailing conservative challenger Pat Toomey by 21 points in a state GOP Primary match-up. He acknowledged becoming a Democrat in part out of fear of losing the party primary.

President Obama, Pennsylvania Governor Edward Rendell and other top Democrats welcomed Specter because it strengthened their party’s majority in the Senate and promised to campaign for his reelection. But Sestak, a retired Navy admiral, opted for a primary challenge, arguing that he is the “real Democrat” in the race.

Rasmussen Reports will release new numbers tomorrow pitting Toomey, the likely 2010 GOP Senate candidate, against both Specter and Sestak.

Twenty-six percent (26%) of likely Democratic Primary voters have a very favorable view of Specter, while 12% regard him very unfavorably. That’s a drop in both numbers from October.

Sestak is seen very favorably by 16% and very unfavorably by just three percent (3%).

At this point in a campaign, Rasmussen Reports considers the number of people with strong opinions more significant than the total favorable/unfavorable numbers.

Specter, who has pledged to vote in favor of the proposed health care reform, leads Sestak by 11 points among those who are insured. He leads by a two-to-one margin (56% to 28%) among those who are not insured.

Not surprisingly, 68% of Democratic Primary voters in Pennsylvania favor the Congressional plan. That figures includes 37% who strongly favor it. Nationally Democrats support the plan much more strongly than Republicans and voters not affiliated with either party,

Sixty-two percent (62%) also think a government-sponsored “public option” to compete with private insurers is a good idea. Just 18% oppose it, with 21% not sure.

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